Electron–hole resonant states in the d=∞ Hubbard model

Abstract

Mean-field limit (d=∞) of the Hubbard model at half filling is investigated within the parquet approach. Simplified parquet equations are explicitly solved at intermediate coupling where nonself-consistent approximations of the FLEX type become numerically unstable. A new solution with anomalous vertex functions (complex effective interaction) was found that is interpreted as a state containing resonant electron–hole pairs.